Mandrel for bending tubing



Oct. 18, 1966 H. K. RADER 3,279,237

MANDREL FOR BENDING TUBING Filed May 20, 1963 2 Sheets-Sheet 1 ZE-INVENTORI Oct. 18, 1966 K, RADER 3,279,237

MANDREL FOR BENDING TUBING Filed May 20, 1963 2 Sheets-Sheet 2 INVENTDR.

Harv/ 7 K Wad United States Patent 3,279,237 MANDREI. FOR BENDING TUBINGHarold K. Raider, Port Huron, Mich, assignor to Mueller Brass (10., PortHuron, Mich, a corporation of Michigan Filed May 20, 1963, Ser. No.281,507 6 Claims. (Cl. 72-466) This invention relates to apparatus foruse in bending tubes, and more particularly to an improvement inmandrels for use in effecting bends in tube blanks by forcing the tubeblanks into an are having the desired configuration.

Heretofore, a conventional method of supporting a tube blank duringbending in a die consisted of filling the tube blank with a low meltingpoint material, such as a ductile metal alloy, prior to forming the tubeinto its bent shape by forcing it into the die. The low melting pointalloy, when solidified, acted as a support to prevent the tubing fromcollapsing during the formation of the bend in the die, and after thetube was bent, the metal alloy was removed by melting the same by theapplication of heat.

It is an important object of the invention to eliminate the necessityfor the use of such metal alloys and the objections incident to its useand to provide a permanent mandrel which will adequately support thetube during the bending operation but which may be quickly and easilywithdrawn from the tube after the forming operation so that it may berepeatedly reused.

Another object of the invention is to provide a mandrel which has therequired flexibility to readily bend with the tubing but which may bewihdrawn from the finished bends.

Another object of the invention is to provide a mandrel of this type,which while flexible, will adequately support the tube againstcollapsing or deformation during the bending operation.

Still another object of the invention is to provide a mandrel of thistype which will eliminate or substantially reduce scratching of theinterior surface of the tube during the bending thereof.

It is still a further object to provide a mandrel having greatmechanical strength and which is capable of maintaining substantiallyunchanged the interior crosssectional dimensions of the tube being bent.

The various objects of the invention, and other ad vantages, areattained by providing a mandrel with a body formed of a plastic materialwhich is substantially incompressible so as to provide adequate lateralsup- V port for the tube during the bending operation but which hassutficient longitudinal flexibility to readily bend with the tubing asthe blank is bent and which has sufficient longitudinal strength topermit it to be Withdrawn from the finished bend.

The various objects and advantages, and the novel details ofconstruction of two practical embodiments of the invention will becomemore apparent from the following description, the appended claims andthe accompanying drawings, in which:

FIGURE 1 is a plan view showing a die and a tube blank on the mandrel inits preliminary position during the bending process;

FIGURE 2 is an end elevational view of the die in closed position, thesame being reduced in size;

FIGURE 3 is a fragmentary view showing the die and the mandrel and tubeblank in an intermediate position during the bending process;

FIGURE 4 is an enlarged longitudinal sectional view of the mandrel;

FIGURE 5 is a fragmentary sectional view taken 3,279,237 Patented Oct.18, I966 substantially on the plane indicated by line 5-5 in FIGURE 4;

FIGURE 6 is a side elevational view of the nosepiece of the mandrel;

FIGURE 7 is a view of the nosepiece looking in the direction of thearrow '7 in FIGURE 6;

FIGURE 8 is a view of the nosepiece looking in the direction of thearrow 8 in FIGURE 6;

FIGURE 9 is a view showing a modified form of mandrel with a tube blankon the mandrel; and

FIGURE 10 is an enlarged transverse sectional view taken substantiallyon the plane indicated by line Iii-10 in FIGURE 9.

Referring to the drawings and more particularly to FIGURES 1, 2 and 3, aconventional die 10 is illustrated which comprises a lower die member 11and an upper die member 12 adapted to be clamped together and havingconfronting recesses to form a die cavity 13. The die cavity shown is ofa shape to form a conven tional elbow.

The tube blank 15, which is to be formed into the elbow, is shown asprovided with a closed end 16 to prevent the extrusion of the mandrel 20through the tube blank during the forming operation. However, it will beunderstood that instead of a closed end 16, the end may be onlypartially closed. The mandrel 20 shown in FIGURES 1 to 8 of the drawingscomprises an elongated body 21 which is formed of a plastic material orof any other suitable type material which is relatively incompressible.In practice, it has been found that a plastic material of thepolyurethane type is particularly adaptable for forming the body portion21.

The material of the body portion 21 is relatively incompressible so asto provide adequate lateral support for the tube blank 15 during thebending operation. The material should also be suflicientlylongitudinally flexible to readily bend with the tube as the blank isbent.

At one end of the body 21 a rounded nosepiece 22 is provided preferablyformed of metal or other relatively hard material. This nosepiece 22 asshown particularly in FIGURES 6, 7 and 8, is provided with an opening orcutaway portion 23 adapted to receive a link of a connecting chain, yetto be described. The nosepiece is provided wih two lugs 24 which definethe opening 23, and the adjacent material of the nosepiece is cut awayas at 25 to provide clearance for the chain link which is to be securedwithin the opening 23. In the embodiment illustrated, the nosepiece isprovided with a recess 44 which enables the nosepiece to be centeredduring its fabrication.

A flexible chain is imbedded in the body 21 and has an end link 31thereof located in the opening or cutaway portion 23. This link issecured to the nosepiece by means of an anchor pin 32 which extendsthrough a transversely extending aperture 33 in the nosepiece whichintersects the opening 23. Thus, the end link 31 of the chain is mountedin the opening 23 for relative pivotal movement with respect thereto asthe nosepiece 22 travels around the bend in the die cavity 13.

The other end of the chain 30 has its end link 34 connected to a base35. This link 34 extends through bifurcations 36 projecting from thebase and is secured in place by an anchor pin 37 passing through thebifurcations and intersecting the end link 34.

The base is secured to a plunger or ram 40 as, for instance, by having athreaded stud 41 thereon engaging a threaded opening 42 in the plungeror ram 4t). The base 35 is provided with an annular forwardly presentedshoulder 43 which engages the end of the body 21 so that u) when theplunger or ram 40 moves forward, the mandrel 20 will move from theposition shown in FIGURE 1 to that shown in FIGURE 3 so as to push themandrel 2t} and tube blank into the die cavity 13. It will be understoodthat this movement is continued until the tube bending operation iscomplete and the elbow is formed.

With the mandrel thus far described, it will be apparent that the tubeblank 15 and mandrel are inserted as a. unit into the die cavity andpushed therein until the forming operation is complete. During thistime, the relatively incompressible material of the body 221 providesadequate lateral support for the tube to prevent collapsing ordeformation thereof, the material of the body 21 having sufiicientlongitudinal flexibility to readily bend with the tubing as the blank isbent. When the bending operation is completed, the plunger or ram isretracted and through the chain 30 the mandrel is withdrawn so that itis then ready for the next bending operation. The closed or partiallyclosed end portion of the tubing is thereafter out ofl thereby formingan elbow open at each end which may thereafter be further processed asdesired to form a finished product.

In FIGURES 8 and 9, a modified form of construction is illustrated. Inthis form of construction, the mandrel comprises a body 50 upon whichthe tube blank 115 is placed. The reference character 51 indicates thebase or pressure applying member which is connected by a threadedportion 52 with a movable portion 53 of a ram mechanism (not shown). Thebase 51 is anchored to the mandrel body 50 by having aperturedprojections 54 provided with apertures 55 imbedded in the body. In thismanner, the mandrel body 50 and the base 51 are integrated.

The mandrel body 50 is provided with a chamber 56 connected by apassageway 57 to a passageway 58 formed in the ram 53. Connected to thepassageway 58 is a supply conduit 59 for supplying fluid under pressureto the charm ber 56. The reference character 60 indicates a return lineby means of which the pressure fluid may be released from the chamber56. Control of the fluid pressure may be accomplished by means of valves61 and 62 provided in the conduits 59 and 60, respectively.

The base 51 may be provided with an annular recess to receive a sealinggasket 63 so as to seal the connection between the ram 53 and base 51against the passage of fluid pressure therebetween.

With this form of construction, the mandrel is expanded and forced intointimate contact with the tubing and is internally supported bysupplying fluid under pressure to the chamber 56 during the formingoperation. After the forming operation is completed, the pressure isreleased from the chamber 56 thereby reducing the diameter of themandrel, and the mandrel may then be withdrawn by retracting the plungeror ram 53.

In this form of construction, the body 50 of the mandrel is preferablymade of a material having the same characteristics as described inconnection with the first form of construction so that the mandrel willprovide lateral support for the tube and will bend longitudinally andfollow the tube blank around the bend in the die cavity. However, inthis form of construction, the lateral support for the tube is providedby the pressure in the chamber 56.

While preferred embodiments of the invention have been described andillustrated herein, it will be understood that various changes andmodifications may be made without departing from the spirit of theinvention.

What is claimed is:

11. A tube bending mandrel for bending a hollow tube blank having anopen end and an, at least partially, closed opposite end, said mandrelcomprising an elongated body portion adapted to extend into the tubeblank, and a base connected to one end of said body portion, said bodyportion being formed of a relatively flexible plastic-likeincompressible material and being longitudinally flexible, said bodyportion terminating in a nose portion with said body and nose portionsbeing of a size to be generally insertable into the tube blank from itsopen end with said nose portion being of a size to engage the oppositeend of the tube blank.

2. The mandrel of claim 1 with said body portion being cylindrical andhaving a selected cross-section no greater than the cross-sectiondefined by the interior of the tube blank and said nose portion having amaximum cross-section in a plane extending transversely to the axis ofsaid body portion no greater than said selected crosssection.

3. The mandrel of claim 1 with said nose portion being of an inflexibleconstruction and further including flexible connection means connectingsaid nose portion and said base to prevent separation thereof when themandrel is withdrawn from the tube blank.

4. The mandrel of claim 3 with said flexible connection means being achain embedded in said body portion.

5. The mandrel of claim 3 with said base portion having a surfaceportion engageable with said one end of said body portion with saidsurface portion having a crosssection no greater than the cross-sectionof said body portion.

6. The mandrel of claim 1 with said body portion being cylindrical andhaving a selected cross-section no greater than the cross-sectiondefined by the interior surface of the tube blank and said nose portionhaving a maximum cross-section in a plane extending transversely to theaxis of said body portion no greater than said selected crosssection,said nose portion being of an inflexible construction, a flexible chainembedded in said body portion and connecting said nose portion and saidbase to prevent separation thereof when the mandrel is withdrawn fromthe tube blank, said base portion having a surface portion engageablewith said one end of said body portion with said surface portion havinga cross-section no greater than said selected cross-section.

References Cited by the Examiner UNITED STATES PATENTS 406,992 7/1889Burgrin 72-466 1,978,452 10/1934 Flodin 72-466 2,450,580 10/1948Conzelman 72-166 2,918,102 12/1959 Klein 72-166 3,180,130 4/1965 Avera72-465 CHARLES W. LANHAM, Primary Examiner. L. A. LARSON, AssistantExaminer.

1. A TUBE BENDING MANDREL FOR BENDING A HOLLOW TUBE BLANK HAVING AN OPENEND AND AN, AT LEAST PARTIALLY, CLOSED OPPOSITE END, SAID MANDRELCOMPRISING AN ELONGATED BODY PORTION ADAPTED TO EXTEND INTO THE TUBEBLANK, AND A BASE CONNECTED TO ONE END OF SAID BODY PORTION, SAID BODYPORTION BEING FORMED OF A RELATIVELY FLEXIBLE PLASTIC-LIKEINCOMPRESSIBLE MATERIAL AND BEING LONGITUDINALLY FLEXIBLE, SAID BODYPORTION TERMINATING IN A NOSE PORTION WITH SAID BODY AND NOSE PORTIONSBEING OF A SIZE TO BE GENERALLY IN-